1. Field of the Invention
The subject invention relates to the fields of radiant energy and electromagnetic radiation and, more specifically, to the transmission of electromagnetic radiation for illumination and communication, to radio, television, telemetry, remote control, intramural information and education systems, passenger entertainment systems abroad aircraft or other vehicles, and other disciplines of utility for the disclosed invention.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, an inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material.
The spectrum of electromagnetic waves or radiation extends over a vast range of frequencies including such manifestations as light, as well as high-frequency carriers for electric signals. Frequently, electromagnetic radiation is emitted or transmitted in a space for illumination and communication. For instance, a room may be illuminated, while being at the same time traversed by radio waves for telecommunication purposes. In general, electromagnetic radiations of significantly different frequencies do not unfavorably interact with each other in space. However, adverse interactions between methods and apparatus for transmitting electromagnetic radiation of different frequencies occur often and have so far typically been viewed as a species of radio interference.
By way of example, it has been observed that fluorescent or other gas discharge lamps, which emit electromagnetic radiation classified as light, tend to affect adversely radio signal transmissions. Against a background of classification of such disturbances as radio interference, the prior art attempted to attack the problem with electric filtering and conventional shielding techniques. For instance, power line filters were associated with gas discharge lamps in an effort to eliminate such high-frequency disturbances as were believed to having been generated by the gas discharge lamp and proceeding along or radiating from the electric lamp feed lines.
While power line filters are of recognized utility in many applications, they have proved incapable of solving the problem here under consideration, as illustrated by the following example.
Aboard a commercial passenger aircraft, a wireless system was installed for transmitting audio entertainment and sound accompaniment for motion pictures or video programs to passengers accommodated in seats equipped with individual radio receivers.
While entertainment needs of passengers were thus attempted to be met via radio frequency signals transmitted through the passenger section of the aircraft, another form of electromagnetic radiation, namely light, was emitted in the passenger section for illumination purposes as needed. In the interest of economy and efficiency, fluorescent lamps were employed for this purpose. Though the two forms of electromagnetic radiation, namely the radio frequency signals and the light emission did, of course, not as such interfere with each other, given the vast difference in frequency between radio waves and light, a strong interference was nevertheless observed in the form of a disturbing alternating-current hum in the audio signals received and reproduced at various seat locations. Since the mentioned hum had its predominant component at 400 Hz, and since the power supply system of the aircraft provided alternating current at a frequency of 400 Hz, it appeared that the hum in question stemmed in some manner from the aircraft's power supply. After a while, it was observed that the hum disappeared or became negligible when the fluorescent ceiling lights of the aircraft were turned off. The only logical explanation on the basis of existing theory was that the fluorescent fixtures or ballasts in some manner generated a noise signal having a 400 Hz component and finding its way through parts of the power supply system to the wireless entertainment equipment. However, various conventional approaches, including filtering of the fluorescent lamp power supply lines, brought no satisfactory relief, and the entire project was in danger of having to be abandoned.
This would have been very unfortunate, since the currently universally used system for supplying audio information in several channels to seated airline passengers employs a system of wire harnesses extending from a central station in the aircraft to individual program selector and sound transducer units in arm rests of passenger seats. This wire harness system is not only expensive in its implementation and installation, but constitutes a source of increasingly severe trouble to the airline, requiring a disproportionate amount of servicing and trouble-shooting and being particularly vulnerable at the cabin wall/passenger seat interface or cabin floor/passenger seat interface.
Despite these problems, airlines and passengers continue to demand audio distribution systems of the type herein mentioned, not only for the provision of audio entertainment and motion picture or video programm sound accompaniment, but also for the communication of safety instructions, flight information and news items on the ground and in flight as well.
Another example which may be mentioned is the indoor illumination of growing plants with ultraviolet light produced by tubular gas discharge lamps and the simultaneous wireless transmission of signals indicating, for instance, the moisture content or other parameters of the soil in which the plants are grown. In that case, a hum of the above mentioned type could either provoke false readings and control action or necessitate the use of an elaborate filtering or coding system.
Another example stems from the widespread use of neon signs and similar gas discharge structures for the purpose of advertising or designating a product or business. In those instances, interference with radio transmission has been observed, and has falsely been attributed to a type of radio interference traveling along power supply lines.
In the area of communication, wireless telephones are becoming increasinlgy popular. This includes installations in which a telephone connection proceeds from a portion of the subscriber's house to a more remote location of his or her premises. The presence or energized fluorescent or other gas discharge lamps can also entail the above mentioned heretofore unexplained interference.
Given the widespread use of fluorescent lights and other gas discharge lamps and the increasingly frequent utilization of radio and wireless television communications, even on an intramural or relatively short-distance scale, the problem herein illustrated is commensurably widespread and the solutions according to the subject invention and its various aspects are of correspondingly broad utility.